1. Field of the Invention
The present invention pertains to the provision of reliable flip chip plastic or organic semiconductor packages, and to a method of producing the packages. More specifically, the present invention is directed to the removal of graphitic and/or fluorinated organic layers from a semiconductor chip passivation layer surface in the instance that a chip passivation layer includes Si-containing materials, whereby the treated chip is employed to make a flip chip plastic package, providing for an increase in the yield or output thereof.
The surface of an advanced semiconductor chip is typically provided with solder balls and a passivation layer. Generally, the passivation layer may be constituted of silicon nitride, a polyimide, a photosensitive polyimide, or of a benzocyclobutane polymer, whereas the solder balls may consist of a Pb and Sn alloy or a Pb-free alloy, whereby the major metallic component of the latter is tin (Sn). The most recently employed semiconductor chips have a tendency to be equipped with Pb-free solder balls in order to protect the environment. In the process of producing the Pb-free solder balls, the surface of a polymer passivation layer, which is provided, includes a graphitic organic layer and/or a fluorinated organic layer.
In a process of manufacturing flip chip plastic ball grid array (FC-PBGA), a chip is placed onto and electrically connected with a laminate, in which flux is employed in the flip chip-joining step, and the subsequently formed residue is ordinarily cleaned with DI water. However, a graphitic layer and/or a fluorinated layer, which is present on the surface of a chip passivation layer, render the post-chip joint cleaning process difficult to implement, whereby a certain level of organotin residue, which is formed during chip joining process remains in an uncleaned condition.
The gap, which remains between a chip and a laminate in an FC-PBGA package, is filled with an underfill material in order to reinforce the mechanical and electrical strength and operational integrity of the FC-PBGA package. The underfill-chip interface evidences a tendency to delaminate in the presence of some level of organotin residue. In that instance, the delamination frequently leads to an extrusion of solder so as to form a tin bridge between adjacent solder balls, thereby resulting in electrical shorts. In addition thereto, the presence of a graphitic layer on a chip passivation layer can also cause electrical shorts, inasmuch as it is electrically conductive in nature.
2. Discussion of the Prior Art
In view of the above-mentioned difficulties, it, thus, becomes necessary to remove the graphitic layer and/or fluorinated polymer layer in order to be able to obtain a clean polymer passivation layer surface, whereby the resultant clean passivation layer surface provides a reliable FC-PBGA electronic package. Oxygen (O2) plasma can readily remove a graphitic and/or fluorinated organic layer. However, O2 plasma processes create SiO2 particles on a photosensitive polyimide (PSPI) and a poly (benzocyclobutane-siloxane) (BCB) since they contain silane compounds. It is well known that O2 plasma on a polymer with silane organic compounds cumulates SiO2 particles on the polymer surface since the plasma forms SiO2 while the polymer is etched. The use of a N2 and H2 mixture gas tends to leave some graphitic layers since H2 plasma reduces organic molecules.